compiler/rustc_ast_lowering/src/path.rs

   1 use crate::ImplTraitPosition;
   2
   3 use super::errors::{GenericTypeWithParentheses, UseAngleBrackets};
   4 use super::ResolverAstLoweringExt;
   5 use super::{GenericArgsCtor, LifetimeRes, ParenthesizedGenericArgs};
   6 use super::{ImplTraitContext, LoweringContext, ParamMode};
   7
   8 use rustc_ast::{self as ast, *};
   9 use rustc_hir as hir;
  10 use rustc_hir::def::{DefKind, PartialRes, Res};
  11 use rustc_hir::GenericArg;
  12 use rustc_span::symbol::{kw, Ident};
  13 use rustc_span::{BytePos, Span, DUMMY_SP};
  14
  15 use smallvec::smallvec;
  16
  17 impl<'a, 'hir> LoweringContext<'a, 'hir> {
  18     #[instrument(level = "trace", skip(self))]
  19     pub(crate) fn lower_qpath(
  20         &mut self,
  21         id: NodeId,
  22         qself: &Option<QSelf>,
  23         p: &Path,
  24         param_mode: ParamMode,
  25         itctx: ImplTraitContext,
  26     ) -> hir::QPath<'hir> {
  27         let qself_position = qself.as_ref().map(|q| q.position);
  28         let qself = qself.as_ref().map(|q| self.lower_ty(&q.ty, itctx));
  29
  30         let partial_res =
  31             self.resolver.get_partial_res(id).unwrap_or_else(|| PartialRes::new(Res::Err));
  32
  33         let path_span_lo = p.span.shrink_to_lo();
  34         let proj_start = p.segments.len() - partial_res.unresolved_segments();
  35         let path = self.arena.alloc(hir::Path {
  36             res: self.lower_res(partial_res.base_res()),
  37             segments: self.arena.alloc_from_iter(p.segments[..proj_start].iter().enumerate().map(
  38                 |(i, segment)| {
  39                     let param_mode = match (qself_position, param_mode) {
  40                         (Some(j), ParamMode::Optional) if i < j => {
  41                             // This segment is part of the trait path in a
  42                             // qualified path - one of `a`, `b` or `Trait`
  43                             // in `<X as a::b::Trait>::T::U::method`.
  44                             ParamMode::Explicit
  45                         }
  46                         _ => param_mode,
  47                     };
  48
  49                     let parenthesized_generic_args = match partial_res.base_res() {
  50                         // `a::b::Trait(Args)`
  51                         Res::Def(DefKind::Trait, _) if i + 1 == proj_start => {
  52                             ParenthesizedGenericArgs::Ok
  53                         }
  54                         // `a::b::Trait(Args)::TraitItem`
  55                         Res::Def(DefKind::AssocFn, _)
  56                         | Res::Def(DefKind::AssocConst, _)
  57                         | Res::Def(DefKind::AssocTy, _)
  58                             if i + 2 == proj_start =>
  59                         {
  60                             ParenthesizedGenericArgs::Ok
  61                         }
  62                         // Avoid duplicated errors.
  63                         Res::Err => ParenthesizedGenericArgs::Ok,
  64                         // An error
  65                         _ => ParenthesizedGenericArgs::Err,
  66                     };
  67
  68                     self.lower_path_segment(
  69                         p.span,
  70                         segment,
  71                         param_mode,
  72                         parenthesized_generic_args,
  73                         itctx,
  74                     )
  75                 },
  76             )),
  77             span: self.lower_span(
  78                 p.segments[..proj_start]
  79                     .last()
  80                     .map_or(path_span_lo, |segment| path_span_lo.to(segment.span())),
  81             ),
  82         });
  83
  84         // Simple case, either no projections, or only fully-qualified.
  85         // E.g., `std::mem::size_of` or `<I as Iterator>::Item`.
  86         if partial_res.unresolved_segments() == 0 {
  87             return hir::QPath::Resolved(qself, path);
  88         }
  89
  90         // Create the innermost type that we're projecting from.
  91         let mut ty = if path.segments.is_empty() {
  92             // If the base path is empty that means there exists a
  93             // syntactical `Self`, e.g., `&i32` in `<&i32>::clone`.
  94             qself.expect("missing QSelf for <T>::...")
  95         } else {
  96             // Otherwise, the base path is an implicit `Self` type path,
  97             // e.g., `Vec` in `Vec::new` or `<I as Iterator>::Item` in
  98             // `<I as Iterator>::Item::default`.
  99             let new_id = self.next_id();
 100             self.arena.alloc(self.ty_path(new_id, path.span, hir::QPath::Resolved(qself, path)))
 101         };
 102
 103         // Anything after the base path are associated "extensions",
 104         // out of which all but the last one are associated types,
 105         // e.g., for `std::vec::Vec::<T>::IntoIter::Item::clone`:
 106         // * base path is `std::vec::Vec<T>`
 107         // * "extensions" are `IntoIter`, `Item` and `clone`
 108         // * type nodes are:
 109         //   1. `std::vec::Vec<T>` (created above)
 110         //   2. `<std::vec::Vec<T>>::IntoIter`
 111         //   3. `<<std::vec::Vec<T>>::IntoIter>::Item`
 112         // * final path is `<<<std::vec::Vec<T>>::IntoIter>::Item>::clone`
 113         for (i, segment) in p.segments.iter().enumerate().skip(proj_start) {
 114             let hir_segment = self.arena.alloc(self.lower_path_segment(
 115                 p.span,
 116                 segment,
 117                 param_mode,
 118                 ParenthesizedGenericArgs::Err,
 119                 itctx,
 120             ));
 121             let qpath = hir::QPath::TypeRelative(ty, hir_segment);
 122
 123             // It's finished, return the extension of the right node type.
 124             if i == p.segments.len() - 1 {
 125                 return qpath;
 126             }
 127
 128             // Wrap the associated extension in another type node.
 129             let new_id = self.next_id();
 130             ty = self.arena.alloc(self.ty_path(new_id, path_span_lo.to(segment.span()), qpath));
 131         }
 132
 133         // We should've returned in the for loop above.
 134
 135         self.diagnostic().span_bug(
 136             p.span,
 137             &format!(
 138                 "lower_qpath: no final extension segment in {}..{}",
 139                 proj_start,
 140                 p.segments.len()
 141             ),
 142         );
 143     }
 144
 145     pub(crate) fn lower_path_extra(
 146         &mut self,
 147         res: Res,
 148         p: &Path,
 149         param_mode: ParamMode,
 150     ) -> &'hir hir::Path<'hir> {
 151         self.arena.alloc(hir::Path {
 152             res,
 153             segments: self.arena.alloc_from_iter(p.segments.iter().map(|segment| {
 154                 self.lower_path_segment(
 155                     p.span,
 156                     segment,
 157                     param_mode,
 158                     ParenthesizedGenericArgs::Err,
 159                     ImplTraitContext::Disallowed(ImplTraitPosition::Path),
 160                 )
 161             })),
 162             span: self.lower_span(p.span),
 163         })
 164     }
 165
 166     pub(crate) fn lower_path(
 167         &mut self,
 168         id: NodeId,
 169         p: &Path,
 170         param_mode: ParamMode,
 171     ) -> &'hir hir::Path<'hir> {
 172         let res = self.expect_full_res(id);
 173         let res = self.lower_res(res);
 174         self.lower_path_extra(res, p, param_mode)
 175     }
 176
 177     pub(crate) fn lower_path_segment(
 178         &mut self,
 179         path_span: Span,
 180         segment: &PathSegment,
 181         param_mode: ParamMode,
 182         parenthesized_generic_args: ParenthesizedGenericArgs,
 183         itctx: ImplTraitContext,
 184     ) -> hir::PathSegment<'hir> {
 185         debug!("path_span: {:?}, lower_path_segment(segment: {:?})", path_span, segment,);
 186         let (mut generic_args, infer_args) = if let Some(ref generic_args) = segment.args {
 187             match **generic_args {
 188                 GenericArgs::AngleBracketed(ref data) => {
 189                     self.lower_angle_bracketed_parameter_data(data, param_mode, itctx)
 190                 }
 191                 GenericArgs::Parenthesized(ref data) => match parenthesized_generic_args {
 192                     ParenthesizedGenericArgs::Ok => self.lower_parenthesized_parameter_data(data),
 193                     ParenthesizedGenericArgs::Err => {
 194                         // Suggest replacing parentheses with angle brackets `Trait(params...)` to `Trait<params...>`
 195                         let sub = if !data.inputs.is_empty() {
 196                             // Start of the span to the 1st character of 1st argument
 197                             let open_param = data.inputs_span.shrink_to_lo().to(data
 198                                 .inputs
 199                                 .first()
 200                                 .unwrap()
 201                                 .span
 202                                 .shrink_to_lo());
 203                             // Last character position of last argument to the end of the span
 204                             let close_param = data
 205                                 .inputs
 206                                 .last()
 207                                 .unwrap()
 208                                 .span
 209                                 .shrink_to_hi()
 210                                 .to(data.inputs_span.shrink_to_hi());
 211
 212                             Some(UseAngleBrackets { open_param, close_param })
 213                         } else {
 214                             None
 215                         };
 216                         self.tcx.sess.emit_err(GenericTypeWithParentheses { span: data.span, sub });
 217                         (
 218                             self.lower_angle_bracketed_parameter_data(
 219                                 &data.as_angle_bracketed_args(),
 220                                 param_mode,
 221                                 itctx,
 222                             )
 223                             .0,
 224                             false,
 225                         )
 226                     }
 227                 },
 228             }
 229         } else {
 230             (
 231                 GenericArgsCtor {
 232                     args: Default::default(),
 233                     bindings: &[],
 234                     parenthesized: false,
 235                     span: path_span.shrink_to_hi(),
 236                 },
 237                 param_mode == ParamMode::Optional,
 238             )
 239         };
 240
 241         let has_lifetimes =
 242             generic_args.args.iter().any(|arg| matches!(arg, GenericArg::Lifetime(_)));
 243         if !generic_args.parenthesized && !has_lifetimes {
 244             self.maybe_insert_elided_lifetimes_in_path(
 245                 path_span,
 246                 segment.id,
 247                 segment.ident.span,
 248                 &mut generic_args,
 249             );
 250         }
 251
 252         let res = self.expect_full_res(segment.id);
 253         let hir_id = self.lower_node_id(segment.id);
 254         debug!(
 255             "lower_path_segment: ident={:?} original-id={:?} new-id={:?}",
 256             segment.ident, segment.id, hir_id,
 257         );
 258
 259         hir::PathSegment {
 260             ident: self.lower_ident(segment.ident),
 261             hir_id,
 262             res: self.lower_res(res),
 263             infer_args,
 264             args: if generic_args.is_empty() && generic_args.span.is_empty() {
 265                 None
 266             } else {
 267                 Some(generic_args.into_generic_args(self))
 268             },
 269         }
 270     }
 271
 272     fn maybe_insert_elided_lifetimes_in_path(
 273         &mut self,
 274         path_span: Span,
 275         segment_id: NodeId,
 276         segment_ident_span: Span,
 277         generic_args: &mut GenericArgsCtor<'hir>,
 278     ) {
 279         let (start, end) = match self.resolver.get_lifetime_res(segment_id) {
 280             Some(LifetimeRes::ElidedAnchor { start, end }) => (start, end),
 281             None => return,
 282             Some(_) => panic!(),
 283         };
 284         let expected_lifetimes = end.as_usize() - start.as_usize();
 285         debug!(expected_lifetimes);
 286
 287         // Note: these spans are used for diagnostics when they can't be inferred.
 288         // See rustc_resolve::late::lifetimes::LifetimeContext::add_missing_lifetime_specifiers_label
 289         let elided_lifetime_span = if generic_args.span.is_empty() {
 290             // If there are no brackets, use the identifier span.
 291             // HACK: we use find_ancestor_inside to properly suggest elided spans in paths
 292             // originating from macros, since the segment's span might be from a macro arg.
 293             segment_ident_span.find_ancestor_inside(path_span).unwrap_or(path_span)
 294         } else if generic_args.is_empty() {
 295             // If there are brackets, but not generic arguments, then use the opening bracket
 296             generic_args.span.with_hi(generic_args.span.lo() + BytePos(1))
 297         } else {
 298             // Else use an empty span right after the opening bracket.
 299             generic_args.span.with_lo(generic_args.span.lo() + BytePos(1)).shrink_to_lo()
 300         };
 301
 302         generic_args.args.insert_many(
 303             0,
 304             (start.as_u32()..end.as_u32()).map(|i| {
 305                 let id = NodeId::from_u32(i);
 306                 let l = self.lower_lifetime(&Lifetime {
 307                     id,
 308                     ident: Ident::new(kw::UnderscoreLifetime, elided_lifetime_span),
 309                 });
 310                 GenericArg::Lifetime(l)
 311             }),
 312         );
 313     }
 314
 315     pub(crate) fn lower_angle_bracketed_parameter_data(
 316         &mut self,
 317         data: &AngleBracketedArgs,
 318         param_mode: ParamMode,
 319         itctx: ImplTraitContext,
 320     ) -> (GenericArgsCtor<'hir>, bool) {
 321         let has_non_lt_args = data.args.iter().any(|arg| match arg {
 322             AngleBracketedArg::Arg(ast::GenericArg::Lifetime(_))
 323             | AngleBracketedArg::Constraint(_) => false,
 324             AngleBracketedArg::Arg(ast::GenericArg::Type(_) | ast::GenericArg::Const(_)) => true,
 325         });
 326         let args = data
 327             .args
 328             .iter()
 329             .filter_map(|arg| match arg {
 330                 AngleBracketedArg::Arg(arg) => Some(self.lower_generic_arg(arg, itctx)),
 331                 AngleBracketedArg::Constraint(_) => None,
 332             })
 333             .collect();
 334         let bindings = self.arena.alloc_from_iter(data.args.iter().filter_map(|arg| match arg {
 335             AngleBracketedArg::Constraint(c) => Some(self.lower_assoc_ty_constraint(c, itctx)),
 336             AngleBracketedArg::Arg(_) => None,
 337         }));
 338         let ctor = GenericArgsCtor { args, bindings, parenthesized: false, span: data.span };
 339         (ctor, !has_non_lt_args && param_mode == ParamMode::Optional)
 340     }
 341
 342     fn lower_parenthesized_parameter_data(
 343         &mut self,
 344         data: &ParenthesizedArgs,
 345     ) -> (GenericArgsCtor<'hir>, bool) {
 346         // Switch to `PassThrough` mode for anonymous lifetimes; this
 347         // means that we permit things like `&Ref<T>`, where `Ref` has
 348         // a hidden lifetime parameter. This is needed for backwards
 349         // compatibility, even in contexts like an impl header where
 350         // we generally don't permit such things (see #51008).
 351         let ParenthesizedArgs { span, inputs, inputs_span, output } = data;
 352         let inputs = self.arena.alloc_from_iter(inputs.iter().map(|ty| {
 353             self.lower_ty_direct(ty, ImplTraitContext::Disallowed(ImplTraitPosition::FnTraitParam))
 354         }));
 355         let output_ty = match output {
 356             FnRetTy::Ty(ty) => {
 357                 self.lower_ty(&ty, ImplTraitContext::Disallowed(ImplTraitPosition::FnTraitReturn))
 358             }
 359             FnRetTy::Default(_) => self.arena.alloc(self.ty_tup(*span, &[])),
 360         };
 361         let args = smallvec![GenericArg::Type(self.arena.alloc(self.ty_tup(*inputs_span, inputs)))];
 362         let binding = self.output_ty_binding(output_ty.span, output_ty);
 363         (
 364             GenericArgsCtor {
 365                 args,
 366                 bindings: arena_vec![self; binding],
 367                 parenthesized: true,
 368                 span: data.inputs_span,
 369             },
 370             false,
 371         )
 372     }
 373
 374     /// An associated type binding `Output = $ty`.
 375     pub(crate) fn output_ty_binding(
 376         &mut self,
 377         span: Span,
 378         ty: &'hir hir::Ty<'hir>,
 379     ) -> hir::TypeBinding<'hir> {
 380         let ident = Ident::with_dummy_span(hir::FN_OUTPUT_NAME);
 381         let kind = hir::TypeBindingKind::Equality { term: ty.into() };
 382         let args = arena_vec![self;];
 383         let bindings = arena_vec![self;];
 384         let gen_args = self.arena.alloc(hir::GenericArgs {
 385             args,
 386             bindings,
 387             parenthesized: false,
 388             span_ext: DUMMY_SP,
 389         });
 390         hir::TypeBinding {
 391             hir_id: self.next_id(),
 392             gen_args,
 393             span: self.lower_span(span),
 394             ident,
 395             kind,
 396         }
 397     }
 398 }